Implantable medical devices that electronically monitor cardiac activity are desirable for a variety of purposes. Some such devices undergo, for various reasons, monitoring operations in which sensing and detection of cardiac events may be temporarily suspended or in which a sensing vector comes into use after a period of disuse. For example, an implantable cardioverter-defibrillator (ICD) may use a blanking period following delivery of an electrical stimulus. On return from the blanking period, reestablishment of a baseline for small-signal sensing of cardiac activity in a predictable and quick manner is desired.